1999 3.0 won't start, Ob2 won't connect to PCM,

[Jay11]

'99 3.0 4x4 83k miles.

Sits mostly, used to start it once a month but last November just wouldn't start. Have retried a couple of times and decided to get into it. It will crank over and over, strongly but not start. Installed a new crankshaft sensor, same result. Squirted starting fluid and it started but for only 3 seconds. I don't hear the fuel pump either. Inserted OBD2 reader and Torque pro gave the error "not connected to OBD interface. Connect then try again." After researching apparently there's a problem with the electrical system that is shutting power off to the computer system that is then preventing power . to the fuel pump. All fuses are good. Swapped all possible relays, all good.-like horn, blower, works when i move the relays around. What should I do next?

 

[Curious Hound]

First, need to check and make sure you have good clean and tight connections for voltage and grounds with no corrosion. Make sure battery is charged. We'll concentrate on starting, first. The OBD II issue may get resolved in the process. Or it may be a separaye issue.

The PCM must energize the PCM relay which sends power to energize the fuel pump relay, which then sends power to the fuel pump through the safety inertia switch. We can bypass the fuel pump relay with a jumper and make the fuel pump run, if it's good. It would be good to make sure you have full battery voltage at the fuel pump relay if you have a voltmeter.

The inertia switch is normally mounted to the firewall in the passenger side footwell. You may have to pull the top edge of the carpet back to see it. There is a reset button you can push to make sure it isn't tripped.

 

[Jay11]

The battery is a good agm type from my f150, it sits charging and drop it in while starting. Inertia switch is aok, pressed down. I will do the other checks tonight.

 

[RobWigglezz]

Do you see the red theft light flashing when trying to start it? Can't remember the exact years, but the PATS will allow it to crank and disable fuel pump if it doesn't recognize the key.

 

[Jay11]

Theft goes off when I turn the key to ON. When I turn key to off or even remove key THEFT keeps blinking constantly once every second indefinitely.
Here are the tests....
PCM relay has power @pin 87&30, probes pushed into those.
Fuel relay has no power with or without key turned to ON position
I jumped the fuel relay pins 87&30 and same behavior - cranked, turned over but never started.
By now battery is jumped to the idling F150 to make sure bat has enough juice.
I toggled inertia switch and pushed it down, result was still the same.

PCM RELAY TESTED

FUEL RELAY Jumped

 

[Curious Hound]

I don't have a diagram with PATS handy. This sounds like either PATS or bad fuel pump or mouse chewed the wirung to the fuel pump.

With the fuel pump relay jumpered the way you have it shown, measure voltage to ground at the inertia switch.

 

[RobWigglezz]

Have you looked around charm.li ? Good resource for finding splice locations, connectors, grounds, electrical diagrams ect.

 

[Curious Hound]

Have you looked around charm.li ? Good resource for finding splice locations, connectors, grounds, electrical diagrams ect.

I just buy the wiring diagram books / EVTMs for my vehicles.

 

[Jay11]

charm.li

That website is impressive! Thanks!

I pulled the inertia switch loom to run some tests. Connector has 3 wires,
#1-on left green/yellow trace-12V input from fuel pump pin 87
#2-red in middle truck airbag/restraint control module
#3-on right brown/L.blue trace switched power to fuel pump
Jumped 1&3, turn key to on, no FP sound.

Used MM tested #1 with truck ground
Key on, Got 12.07v, then drops to 6.85v

Jumped #1&#3, probed #1 & ground
Key on, Got 12.57v then drops to 12.34v

Next tested wire continuity from IS to FP.
Probed 3 with ground, DMM set to 200 ohms, got 127.3 ohms. Apparently this confirms that the plug connector to the FP is bad to the unusually high resistance. And if that is ok then this proves FP is bad. Do you guys agree? If so,...

Is there a way to access the FP connector to unplug and clean with electronic spray, short of pulling off the truck bed or dropping the fuel tank?

 

[Curious Hound]

Next tested wire continuity from IS to FP.
Probed 3 with ground, DMM set to 200 ohms, got 127.3 ohms. Apparently this confirms that the plug connector to the FP is bad to the unusually high resistance. And if that is ok then this proves FP is bad. Do you guys agree? If so,...

That might be the resistance of the fuel pump windings. That could be a good reading. I don't have time to get a comparison reading right now.

Even though those resistance readings aren't what I expected, it still sounds like a bad fuel pump. You don't have to pull the bed completely off the truck. Just remove the bolts and lift the front up. Prop it securely on both frame rails and you can get to the top of the tank. I leave the 2 rear bolts in their holes, loosely to keep the bed from sliding off the back.

 

[Jay11]

Tonight I pulled the bed off just enough to get to the pump. I was expecting to find a badly corroded connector but instead found a super clean unit from very good protection. I will grab a pig tail tomorrow and test continuity on the pump itself. For now I don't know what the discovery of the clean unit weighted against previous reading of 127.3 Ohms means.